1. Field of Invention
The present invention generally relates to wireless communication devices that are configured to provide for combined operation of a plurality of wireless protocols covering different parts of the frequency spectrum, and more particularly for transmitting LTE (long term evolution mode), CDMA (code division multiple access), UMTS (universal mobile telecommunications system), and GSM (global system for mobile communications) signals originated from different base stations BTS's (or transceivers) from a common antenna.
2. Description of Related Art
Continuing progress in wireless communications produces new and more sophisticated protocols that provide new services, which were not previously available. Implementation of these new technologies requires their collocation with the old base station technologies that are currently in use on the same site.
There are three commonly used methods for adding new services (e.g., LTE, UMTS, or WCDMA) to existing sites with existing BTS equipment (e.g. GSM or CDMA). The first method is to install additional antennas on the tower and run new feeder cables to connect to the new base station that is providing the new services (LTE, UMTS or WCDMA). This simple method results in additional tower loading that may require significant expense. In many cases, the incremental costs can be prohibitive or the addition of feeders and antenna's may be simply physically impossible. This is especially true at sites where several carriers are collocated.
The second method, which is widely used in the industry, utilizes multi-port hybrid combiners with operating bandwidths wide enough to accommodate the operation of the new services (LTE, UMTS or WCDMA channels) and existing services (GSM or CDMA channels). The drawback of this method is the significant insertion loss which is typically proportional to the number of channels connected to the corresponding ports of the combiner. These losses are caused by the non-coherent nature of the independent RF power sources (channels) connected to the hybrid combiner's input ports. As a result, most of the power is dissipated in the internal loads of the combiner which results in a significant loss of coverage at the site.
The third established method utilizes Multi-Channel Power Amplifier (MCPA) technology to combine multiple transmitters onto a common feeder line. The gain of this amplifier compensates for the losses of the hybrid combining which typically occurs ahead of the MCPA. However, in order to satisfy the linearity and power requirements of this type of operation, MCPA's must implement sophisticated linearization techniques including predistortion and/or feed-forward technologies, which make them complex and cost-prohibitive.